In the manufacture of flashlamp arrays and particularly multi-lamp flashlamp arrays it is a common practice to enclose the array within a plastic cover. This plastic cover serves not only to provide structural integrity but also provides security from injury for the consumer. In both cases, structural integrity and consumer security, mechanical or chemical bonding of the plastic cover is an essential ingredient.
Bonding of flashlamp arrays employing mechanical and chemical techniques such as hot-melt adhesives and glues has been found to be somewhat less than satisfactory in high production operations for numerous reasons. For example, most adhesives and glues tend to be cumbersome to handle at best and chemical bonding in general tends toward the undesired presence of toxic and often flammable conditions. However, such techniques have been and still are utilized with varying degrees of success.
Other bonding techniques include heat sealing of plastic surfaces and ultrasonic sealing of plastic surfaces for example. In a heat sealing process, it is common to position a pair of layers of plastic in contact with one another and to apply heat thereto in an amount sufficient to melt the plastic layers such that they are welded to one another. Unfortunately, heat sealing is often dependent upon heat from high temperature lamps which tend to exhibit life problems, cooling problems and replacement problems. Also, the plastic must be such that it absorbs heat in an amount sufficient to soften the plastic and then cools at a rate which corresponds to a desired rate of production.
On the other hand, ultrasonic bonding is dependent upon the transformation of sonic energy into friction and heat by the mechanical movement of the plastic layers with respect to one another. As a result, the plastic layers must have similar characteristics, a low melting temperature and good conduct therebetween because of the limited vibratory movement of the plastic layers.
Importantly, the known multi-lamp photoflash arrays include a pair of flat and smooth plastic surfaces in contact with one another and enclosing the operational components of the array. Thus, heat sealing or ultrasonic bonding is appropriate. However, this type of seal tends to provide a peel-type mode of bonding wherein the seal is subjected to a peal-type stress which is neither flexible nor particularly strong insofar as resistance to pressure is concerned.